Solar power on a homemade floating island is not easy, unless you have the money for photovoltaic panels. But theyre only about 15% efficient. The rest of the Suns energy either bounces back into outer space, or heats the shingles. However if you needs are small, there are plenty of articles on the web about them. I have no need to repeat that here.
On a floating island, energy storage is not as easy. The best way is to store it as water in a water tower. But how do you get the water up there? One way is with evaporation and condensation. Thats the process by which rain is made.
A wind-powered water pump can be easily added to the system to cover times when there is wind, but no sun.
If your boiler and water tower is tight, to prevent air from getting in, water can be made to boil at room temperature, making you system that much more efficient.
If your feed water system inputs seawater, the condensed water is fresh, ready to drink, see my article on distillation at room temperature
Naturally, such a system is your experiment, and neither the author nor the Rocky Mountain Research Center provide any guarantees.
Thanks for your interest.